Transmission system regulation



Aug. 11, 1936. 5 JOHNSON 2,050,703

TRANSMISSION SYSTEM REGULATION Filed June 9, 1954 /Nl/E/v TOR J. B.JOHNSON HVJ A TTORNEV Patented Aug. 11, 1936 UNITED STATES PATENToFaFlcE TRANSMISSION SYSTEM REGULATION Application `lune 9, 1934, SerialNo. 729,738

7 Claims.

The present invention relates to the compensation of variations intransmission characteristic of a circuit occasioned by Variations intemperature. The circuit may, for example, be a telephone line strung onpoles or included in a cable and subject to climatic or atmospherictemperature variations.

An object of the invention is to compensate for the effects oftemperature variations in a simple and direct manner and without thenecessity of using mechanically moving elements.

An ordinary telephone line has a positive and substantially linearvariation of resistance with temperature over the limited range embracedby atmospheric temperatures. In accordance with the present invention anelement having a negative coefficient of resistance is associated with atelephone line and is subjected to the same variations of temperature asis the line itself, such lthat the resistance changes in the line arecompensated by the resistance changes in the element.

The nature of the invention and the manner of carrying out the inventionin practice will now be made clear in the following detaileddescription, taken in connection with the accompanying drawing.

In the drawing:

Fig. 1 is a simplied diagrammatic showing of a telephone line includingrepeater stations and compensating means according to the invention; and

Fig. 1 is a diagram of impedance to be discussed.

In Fig. l, the telephone line I0 may be a toll line included along witha large number of other similar lines inside a lead sheath (not shown).This toll line is shown as including one-way repeaters I I, I2 etc. atintervals, two such repeaters being shown with a length of line I0comprising one repeater section between these repeaters. At some pointalong the line, for example, near the center of the repeater section, acompensating impedance combination I5, i6 is included, or, as shown,such a combination may be placed in each side of the line for symmetry.The compensating impedance combination may be placed at or near eitherend of the line section l0 so long as it is subjected to temperaturevariations similar to the temperature variations experienced by theline. For example, if the cable including line ID is buried or placed ina conduit underground or suspended on a pole line, the compensatingimpedance combination is preferably included inside the lead sheath at apoint along the cable where its temperature changes are representativeof the temperature variations of the cable so far as possible. There maybe several impedance combinations I5, I6 within a repeater section,spaced at intervals.

The compensating impedance combination comprises preferably an elementI5 having a negative coefficient of resistance shunted by a resistanceI6 of positive coefficient, and included in series in the line.

Referring to the diagram in Fig. la, let the element I5 have aresistance fc, the element I0 a resistance y and the line III aresistance z, assuming now that but one such combination is used in theline section I0. In the following treatment, the symbols then have the-following The three resistances y, and z are assumed,

over the temperature range 40 C., to vary with temperature as follows:

In (2), for purposes of simplicity, assume to be so small that y, may beconsidered constant. The resistance of the compensating combination isthen I; XoyofIt Xo-I'yo 'I'he slope of the r, t curve at t=0 is given byThe expression for the second derivative at y The condition thatcompensation be attained at t=0 is that For compensation over a range oftemperatures it is also well to have the second derivative small, say

From (7) We find that the rst condition is fulfilled if CEXOQVO2 From(8) We lnd that the second condition is fulfilled if :co=yo, so thatsubstituting in (9) we have 4 (10) X0= -gzo=y0 Substituting for x and yoin (4),

Mr zo) i (u) (a) ea+1 The ratio,

E p-Z0 can now be calculated.

iQ- l! p *zo* 220 0! Assuming reasonable values as follows,

and 2:1,000 ohms we have 11:1/2, and calculations'indicate the degree ofcompensation possible With this arrangement, viz:

Tempera- Percent ture R R R deviation If y Were placed in series with a:and z, and were constant at such a value that In the shunt example,since p=%, the resistance added to that of the line is 50 per cent ofthe line resistance. The comparison is made with theV series case on thesame basis, but if, in the latter case, yn were zero so that the addedresistance would be 25 per cent of the line resistance, the deviationswould be changed very little.

As examples of materials that are suitable for use in practice and thatbeha-ve in the general manner assumed in the above calculations, theelement I5 may comprise a resistance made of one of the metallic oxidesor sulphides such as zinc oxide or silver sulphide. The element I6 maybe a resistance of very small temperature coefficient such as advancewire.

It is to be understood that the invention is not to be limited to thenumerical values or relations that have been given but its scope isindicated by the claims.

What is claimed is:

1. The combination of a circuit subject to variable temperature, saidcircuit having a positive temperature coe'icient or" resistance, and animpedance combination connected in series in said circuit, subjected tosimilar variable temperature and including elements of differenttemperature coeflicients connected in parallel with each other, one ofthem having a negative temperature coeicient of resistance, theresistance relations of said one element, impe-dance combination andcircuit, and the relation or" temperature coeicients cf said circuit andsaid one element, being such that the combination of circuit andimpedance combination has an overall resistance substantially constantthroughout a range of temperatures.

2. The combination of a telephone line subjected to variable temperatureand an impedance combination serially inserted in the line and subjectedto similar variable temperature, said impedance combination comprisingtwo elements in parallel, one an element having a temperature coeficientof resistance opposite to that of the line, and the other an element ofvery small temperature coefiicient of resistance, said two elementshaving substantially the same resistance at reference temperature, andin parallel presenting an impedance (ro) in the line which bears to theline resistance (Zo) substantially the same numerical relation as twicethe temperature coeiicient of resistance of the line bears to that ofthe rst mentioned element.

3. The combination of a transmission line subjected to variabletemperature and an element serially included in said line and subjectedto the same variable temperature as said line, said element having atemperature coecient of resistance opposite to that of the line wherebyresistance changes of said line and element in response to temperaturevariations tend to compensate one another, and a resistance of smalltemperature coeilcient connected in parallel to said element andproportioned with respect to said element such that the parallelcombination of element and resistance causes the resistance variationsto be more completely compensated than they would be by said elementalone.

4. A combination according to claim 1 in which said one element having anegative temperature coeicient of resistance comprises zinc oxide.

5. A combination according to claim l in which said one element having anegative temperature coeflicient of resistance comprises silversulphide.

6. The combination with a transmission line whose attenuation isvariable with line-tempera- 'said elements are comprised of silversulphide.

J OI-IN B. J OHNSON.A

